1. Field of the Invention
This invention relates to a spin electronic material that exhibits a spin-dependent electronic effect and to a method of fabricating the material.
2. Description of the Prior Art
Much is heard these days about the Information Technology (IT) revolution. This reflects the progressive realization of an information industry supported by dramatic advances in electronics and other technologies. Electronics technologies that enable transmission, reception, accumulation and, when necessary, processing of huge amounts of data have become available as basic technologies of the IT revolution, while intense R. and D. aimed at achieving still further technology breakthroughs is being pursued on a global scale. Against this backdrop, a new field of electronics that makes positive use of the spin attribute of electrons has come into the spotlight. This field, called spin electronics, has emerged for two primary reasons.
The first is its applicability as a storage technology using ferromagnetic materials that exhibit spin polarization at normal room temperatures. Devices utilizing this technology are already in practical use, including, for example, read heads in hard disk drives and the like that use multilayer structures formed of ferromagnetic metals. In addition, nonvolatile magnetic random access memories that utilize the memory effect exhibited by a spin-polarized ferromagnetic material and are capable of storing data without consuming power are also a subject of vigorous R. and D. (See, for example, {circle around (1)}JP-A-2000-40355 and {circle around (2)}JP-A-2000-156531.)
The second is its applicability to the development of quantum communication using spin-polarized electrons. Quantum computers, quantum communications and related technologies utilizing electron spin characteristics have the potential to render marked changes in encryption techniques and, as such, have become the subject of national scale research projects. The injection of spin-polarized electrons from a magnetic semiconductor into Group III-V semiconductors (e.g., GaAs) of the type used in conventional electronics constitutes one unit operation of such quantum communication. That such injection can occur at low temperatures has been substantiated. (See {circle around (1)}Nature, Vol. 402, 787-790 (1999) and {circle around (2)}Nature, Vol. 402, 790-792 (1999).)
New materials are required to support the development of these emerging technologies. While Fe, Co, Ni and alloys of these metals, which are capable of magnetization at normal room temperatures, are used in storage applications, for example, they have a fatal drawback from the aspect of forming heterostructures with Group III-V semiconductors such as GaAs used as photonic materials. Specifically, these elements are incompatible with the Group III-V semiconductor fabrication process because when incorporated in a Group III-V semiconductor, they become electrical impurities and/or new byproducts lacking spin-polarized electrons. (See {circle around (1)}Physics of semiconductor device, S. M. Sze, John Wiley and Sons, Inc. ISBN 0-471-09837-X and {circle around (2)}Magnetic Material Handbook (Asakura Publishing Co., Ltd.), ISBN 4-254-13004-X.)
One promising spin electronic material, currently a subject of active basic-level research, consists of a heterostructure between a Group III-V semiconductor and a compound ferromagnetic material which is composed of Mn and a Group V element and is not of the zincblende type. (See {circle around (1)}Applied Physics Letters, Vol. 68, No. 20, 2890-2892 (1996) and {circle around (2)}Applied Physics Letters, Vol. 70, No. 15, 2046-2048 (1997).) Non-zincblende type materials readily permit incorporation of Mn into Group III-V semiconductors. Since the Mn therefore forms a shallow impurity level and markedly changes the electrical properties of the Group III-V semiconductor, such materials are also incompatible with the Group III-V semiconductor fabrication process. (See Physics of semiconductor device, S. M. Sze, John Wiley and Sons, Inc. ISBN 0-471-09837-X.
Considerable research is also being focused on perovskite oxides (see {circle around (1)}JP-A-9-263495 and {circle around (2)}Nature, Vol. 395, 677-680 (1998)), Cr oxide films (see Applied Physics Letters, Vol. 76, No. 25, 3789-3791 (1997)) and other substances expected to exhibit high ferromagnetic transition temperatures and higher degree of spin polarization. As these are totally different in crystal structure from the semiconductors used in electronics, however, they have fundamentally poor compatibility with semiconductor electronic materials and are therefore extremely difficult to fabricate on a semiconductor substrate.
A group of substances called xe2x80x9cmagnetic semiconductorsxe2x80x9d are also attracting attention as spin electronic materials. The experiments that substantiated the aforesaid injection of spin-polarized electrons were, in fact, conducted using such substances. (See {circle around (1)}Nature, Vol. 402, 787-790 (1999) and {circle around (2)}Nature, Vol. 402, 790-792 (1999).) As the ferromagnetic transition temperature of, for example, the (Ga, Mn)As used in the experiments is at most 120 K, however, use of these substances as practical device materials is substantially impossible. (See Science, Vol. 281, 951-956 (1998).)
The energy level formed when elemental Cr is incorporated in a semiconductor electronic material such as GaAs has been thoroughly researched. (See Physics of semiconductor device, S. M. Sze, John Wiley and Sons, Inc. ISBN 0-471-09837-X.) In particular, Cr is an element commonly used as a dopant for achieving a semi-insulating state in GaAs. While MnP-type CrAs and Cu2Sb-type Cr2As are well known compounds of Cr and As, both are antiferromagnetic materials found to have no path to application as spin electronic materials. (See Magnetic Material Handbook (Asakura Publishing Co., Ltd.), ISBN 4-254-13004-X.) Expressed in the terminology of physics, the magnetic state of CrAs is properly called xe2x80x9chelimagnetism.xe2x80x9d Although ferromagnetism has been reported in a high-order CrAs compound of unknown crystal structure and composition, the ferromagnetic transition temperature of the compound is below 0xc2x0 C. (See Journal of the Physics Society of Japan, Vol. 15, No. 11, 2007-2012, 1960.) In other words, As compounds of Cr have received no attention as spin electronic materials.
Development of new substances that not only exhibit superior properties as materials but also have good compatibility with existing semiconductor electronic materials is desired for promoting progress in the field of spin electronics. The properties of these materials should, at the very minimum, include transition temperature in or exceeding the normal room temperature range and high degree of spin polarization. Compatibility with existing semiconductor electronic materials should desirably be such as to enable sharing of common fabrication processes, fabrication of heterostructures and avoidance of the formation of byproducts that cause property degradation during heterostructure fabrication.
This invention was accomplished in light of the foregoing circumstances and has as an object to provide a spin electronic material exhibiting, as material properties, transition temperature in or exceeding the normal room temperature range and high degree of spin polarization, and having compatibility with existing semiconductor electronic materials such as to enable sharing of common fabrication processes, fabrication of heterostructures and avoidance of the formation of byproducts that cause property degradation during heterostructure fabrication. Another object of this invention is to provide a method of fabricating the spin electronic material.
In order to achieve these objects, the present invention, in a first aspect, provides a spin electronic material exhibiting a spin-dependent electronic effect, which material comprises zincblende TE-VE, where TE stands for V, Cr or Mn and VE stands for As or Sb.
In a second aspect, this invention provides a spin electronic material exhibiting a spin-dependent electronic effect, which material comprises a heterojunction of a zincblende TE-VE, where TE stands for V, Cr or Mn and VE stands for As or Sb, and a zincblende Group III-V semiconductor of GaAs, AlAs, InAs, GaSb, AlSb, InSb or a mixed crystal thereof.
In a third aspect, this invention provides a spin electronic material exhibiting a spin-dependent electronic effect and enabling control of degree of spin polarization, intensity and anisotropy of magnetism, and ferromagnetic transition temperature according to the first or second aspect, wherein the zincblende TE-VE is added with at least one element selected from the group consisting of Li, Be, B, C, N, O, P, Na, Mg, Al, Si, P, S, Cl, K, Ca, Sc, Ti, Fe, Co, Ni, Cu, Zn, Ga, Ge, Se, Br, Rb, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Te, I, Cs, Ba, La, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb and Bi.
In a fourth aspect, this invention provides a spin electronic material exhibiting a spin-dependent electronic effect and enabling control of degree of spin polarization, intensity and anisotropy of magnetism, and ferromagnetic transition temperature, which material comprises a mixed crystal of TE-VE, where TE stands for V, Cr or Mn and VE stands for As or Sb, and a different zincblende TE*-VE* represented by TE1xe2x88x92xTE*x-VE1xe2x88x92yVE*y (where 0xe2x89xa6xxe2x89xa61, 0xe2x89xa6yxe2x89xa61, TE* is V, Cr or Mn and different from TE, and VE* is As or Sb and different from VE).
In a fifth aspect, this invention provides a spin electronic material exhibiting a spin-dependent electronic effect and enabling control of degree of spin polarization, intensity and anisotropy of magnetism, and ferromagnetic transition temperature which material comprises multilayers of zincblende TE-VE, where TE stands for V, Cr or Mn and VE stands for As or Sb, and a zincblende Group III-V semiconductor of GaAs, AlAs, InAs, GaSb, AlSb, InSb or a mixed crystal thereof represented by {[TE-VE]xc3x97d1/[III-V]xc3x97d2}xc3x97N (where [III-V] stands for zincblende Group III-V semiconductor, d1 for thickness of the zincblende Te-Ve, d2 for thickness of the semiconductor and N for repetition period).
In a sixth aspect, this invention provides a method of fabricating a spin electronic material exhibiting a spin-dependent electronic effect comprising the steps of:
retaining a substrate of zincblende semiconductor electronic material at a temperature not exceeding 400xc2x0 C.; and
using a non-thermal equilibrium gas phase growth process to deposit TE-VE, where TE stands for V, Cr or Mn and VE stands for As or Sb, simultaneously on the substrate.
In a seventh aspect, this invention provides a method of fabricating a spin electronic material according to the sixth aspect, wherein the substrate is formed of zincblende GaAs.
In an eighth aspect, this invention provides a method of fabricating a spin electronic material according to the sixth aspect, wherein the TE, when deposited, has a molecular beam equivalent pressure set lower than a VE molecular beam equivalent pressure.
As will be understood from the foregoing, this invention is capable of providing a zincblende TE-VE compound whose crystal structure is the same as that of GaAs or other such semiconductor electronic material.
This TE-VE compound has a transition temperature in or exceeding the normal room temperature range and high degree of spin polarization. It also exhibits good compatibility with existing semiconductor electronic materials, whereby it enables sharing of common fabrication processes, fabrication of heterostructures and avoidance of the formation of byproducts that cause property degradation during heterostructure fabrication. As such, it embodies many properties desired in conventional spin electronic materials and therefore can be expected to find extensive use as a basic material for realizing next-generation information technologies (IT).
The above and other objects and features of the present invention will become apparent from the following description made with reference to the accompanying drawings.